The persistence of the HIV epidemic is largely fueled by risky drug practices and sexual behaviors related to METH use, but robust and modifiable neurobehavioral predictors of HIV transmission risk behaviors have yet to be identified. Deficient social cognition, which represents problems with understanding and regulating one's own emotions as well as with placing oneself in another's shoes cognitively and emotionally, may negatively impact the ability to safely navigate HIV risk situations that occur in these highly social contexts, especially when decision-making abilities are impaired, such as in the case of persons with comorbid HIV/METH who are vulnerable to frontal systems injury. Given the negative effects of aging on social cognition, older HIV+ adults who use METH may be particulariy vulnerable. Project 3 aims to utilize a 2x2 factorial design in a cohort of 320 individuals (identical to those in PI) to investigate the separate and combined effects of HIV and METH on social cognition, as well as potential modulation of these effects by age. Among the risk groups, the incremental value of social cognition as a predictor of HIV transmission risk behaviors and social functioning will be investigated. This project also aims to examine the neurobehavioral, neurobiological, neuroimaging, and animal model correlates of human social cognition through synergy with other Cores and Projects. We will also relate our findings to those of a proposed pilot study (Pilot Project D in PAD Core) that tests a mouse model of social cognition. A theory-driven model of social cognition will be comprehensively evaluated through integration of emotional and cognitive components, which will be rigorously measured with multiple indices balanced across laboratory performance-based tests and self-report measures. This novel, inclusive approach will fully characterize social cognition in this cohort, as well as its relation to vital daily functioning outcomes, which will likely fill a critically important missing link in the prediction of HIV risk behaviors, allowing for targeted intervention aimed at HIV transmission reduction.